150 ANARTHROPODA 



located on either side of the head. In the squids and cuttle- 

 fish the shell is rudimentary and is buried within the 

 mantle, while in the pearly nautilus (Nautilus pompilius) 

 it is in the form of a spiral divided into chambers, the larg- 

 est and outer of which is alone occupied by the animal. 

 As soon as the body becomes 

 too small for one chamber it 

 moves forward, constructing a 

 partition behind it. This is the 

 creature which inspired the cele- 

 brated poem, "The Chambered 

 Nautilus," by Holmes. 



The cephalopods are of little 

 economic importance. The cut- 

 . 176. -Pearly nautilus th tlefish supply sepia for the artist 



half the shell removed. 



and are of some use for food. 

 Squid are used for cod bait along the New England shore. 



ii. VERMES 



The worms form a group of animals not easily defined 

 because of their great variation in structure and habits; 

 therefore, modern zoologists have separated them into sev- 

 eral subkingdoms, of which the three most important are 

 Annulata, Nemathelminthes, and Platyhelminthes. 



Annulata or Segmented Worms 



This phylum is widely represented by leeches and earth- 

 worms. As the habits of the two groups are quite different, 

 each will be described separately. 



Leeches. These are often called bloodsuckers, owing to 



